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Abstract

A novel spectrophone sensor prototype consisting of a T-shaped acoustic microresonator (T-mR) in off-beam quartz-enhanced photoacoustic spectroscopy (T-mR QEPAS) is introduced for the first time. Its performance was evaluated and optimized through an acoustic model and experimental investigation via detection of water vapor in the atmosphere. The present work shows that the use of T-mR in QEPAS based sensor can improve the detection sensitivity by a factor of up to ~30, compared with that using only a bare QTF. This value is as high as that obtained in a conventional “on-beam” QEPAS, while keeping the advantages of “off-beam” QEPAS configuration: it is no longer necessary to couple excitation light beam through the narrow gap between the QTF prongs. In addition, the T-mR is really suitable for mass production with high precision.

Figures (4)

T-shaped mR based QEPAS spectrophone configuration. (a1) 3D map of an ideal T-shaped mR based QEPAS approach; (a2) 3D map of a T-mR made with a cubic aluminum block in the present work; (a3) cross section profile along axis of the main pipe of an ideal T-shaped mR; (a4) orifice formed by a QTF placed as close as possible to the branch pipe end of an ideal T-shaped mR; (a5) setup consisting of an ideal T-shaped mR and a QTF observed from the cross section along axis of the branch pipe.

Theoretical model for calculation of the optimum T-mR parameters. (b1) T-shaped mR and coordinate system; (b2) orifice area Ω1 of the branch pipe end close to the QTF (seen from the axis of the branch pipe and the gap between QTF prongs); (b3) gap (between the QTF and the branch pipe end) district surface area Ω0; (b4) equivalent of a circular orifice (Fig. 2(b4)) to the real non-circular orifice (b2) with an effective area Ω = Ω1.